Mechanical Advantage II

Mechanical Advantage II : 

Mechanical Advantage II

SPECIAL NOTE : 

SPECIAL NOTE The Actual Mechanical Advantage (AMA) will always be less than the Ideal Mechanical Advantage (IMA) because of friction losses: AMA < IMA

The LEVER : 

The LEVER Levers are divided into three classes, depending on the relative arrangement of 1. The fulcrum (the fixed pivot point) 2. The load (the output force). 3. The effort (the input force)

Class 1 : 

Class 1

Class 2 : 

Class 2

Class 3 : 

Class 3 Notice that a class 3 lever is the only one that does not amplify the input force. Rather, it is used to increase the distance that the load is moved, but of course this means that the input force must be larger than the output force.

Slide 8: 

IMA of Levers For levers, the distances that the forces act through are proportional to the lengths of the two lever arms, or Proof: In the figure below, the angles are the same on both sides of the fulcrum, and so the ratio of arc length s to radius r is the same, because . Thus

AMA of LEVERS and Other Machines : 

AMA of LEVERS and Other Machines AMA = Force of weight Force you measure

Wheel and Axle, Pulleys, and Gear : 

Wheel and Axle, Pulleys, and Gear A wheel and axle is really just a lever, because at any instant there is a tangential force on the wheel and axle, acting on a lever arm equal to the radius of the wheel or axle. The long lever arm is the radius of the wheel, and the short lever arm is the radius of the axle. Note that both the wheel and the axle are cylinders.

Slide 11: 

Just as with levers, the mechanical advantage is the ratio of the lever arms, which is this case are the radii: · The ratio of diameters is the same as the ratio of radii, so you can use diameters if it is more convenient.

Systems of Pulleys: The Block and Tackle : 

Systems of Pulleys: The Block and Tackle Lifting a heavy object by running a rope over a fixed pulley does not offer any mechanical advantage. A fixed pulley only changes the direction of the force, allowing you to stand in a convenient place. By adding a movable pulley we can gain mechanical advantage.

Slide 13: 

In the example above, two strands now support the weight, which means that the tension in the rope is half the weight. Of course, the gentleman in the picture now has to move his end of the rope twice as far to move the mass the same distance as before.

Inclined Plane : 

Inclined Plane

The Screw : 

The Screw A screw is a variation of an inclined plane (or a wedge) in which the incline is wrapped around a shaft. The pitch of a screw is the distance between its threads, and this is the distance that the screw will advance with one complete rotation. To calculate to IMA you need to know the pitch, but you also need to know the length of the lever arm being used to turn the screw. This lever arm could be the radius of a screwdriver handle, of the length of the handle on a vise or a C-clamp. This will allow you to calculate how far the screw will advance for a given lever movement.

Slide 17: 

Suppose the lever arm is L and the pitch of the screw threads is p. The trick is to consider one full revolution. For one revolution the end of the lever travels a distance equal to the circumference of the circle :

Slide 19: 

THE END